The present invention relates to a control apparatus for controlling a transmission apparatus that includes: an input member drivably connected to an engine and a rotating electrical machine; an output member drivably connected to wheels; and a speed change mechanism that has a plurality of friction engagement elements that are controlled to be engaged and released so as to switch a plurality of shift speeds, and that shifts the rotation speed of the input member at a gear ratio of each shift speed so as to output the shifted speed to the output member.
As a vehicular driving apparatus provided with a transmission apparatus that includes an input member drivably connected to an engine, an output member drivably connected to the wheels, and a speed change mechanism that has a plurality of friction engagement elements that are controlled to be engaged and released so as to switch a plurality of shift speeds, and that shifts the rotation speed of the input member at a gear ratio of each shift speed so as to output the shifted speed to the output member, the apparatus described in Japanese Patent Application Publication No. JP-A-2002-130453 is known. In such a driving apparatus, generally, when switching between two shift speeds adjacent to each other is performed in a transmission apparatus, engagement and release of the friction engagement elements are controlled so as to carry out a so-called clutch-to-clutch shifting. In the so-called clutch-to-clutch shifting, normally, a friction engagement element to be released is relatively swiftly released fully at an initial stage in the shifting operation, and a friction engagement element to be engaged is gradually engaged while slipping in a semi-engaged state. As a matter of course, this holds true when switching to a shift speed with a smaller gear ratio (an upshift) is carried out in a state where an accelerator pedal position of a vehicle is equal to or smaller than a prescribed value.
In this connection, the transmission apparatus of Japanese Patent Application Publication No. JP-A-2002-130453 is structured such that, when an upshift is carried out in a situation where the accelerator pedal position of the vehicle is equal to or smaller than a prescribed value, a control apparatus exerts release-side friction engagement element control so as to switch a pressure of hydraulic oil on a release-side element, which is a friction engagement element to be released at shift speed switching, between a release ensuring pressure under which the release-side element is brought into a state immediately before engagement and an engagement ensuring pressure under which the release-side element slightly engages. By exerting the release-side friction engagement element control, a downshift operation can immediately be started in response to a determination to downshift (to switch to a shift speed with a greater gear ratio) when upshifting in a situation where an accelerator pedal position of the vehicle is equal to or smaller than a prescribed value. Under the release-side friction engagement element control of Japanese Patent Application Publication No. JP-A-2002-130453, the pressure of hydraulic oil on the release-side element is increased and reduced relative to a stroke end pressure of the release-side element with a prescribed pressure width (ΔP2), thereby being switched between the release ensuring pressure and the engagement ensuring pressure. Under the release-side friction engagement element control, at shift speed switching, the release-side element alternates between a semi-engaged slipping state and a fully released state.
On the other hand, as one exemplary vehicular driving apparatus in which both an engine and a rotating electrical machine are employed as driving force sources for use in a hybrid vehicle, an apparatus described in Japanese Patent Application Publication No. JP-A-2008-094332 is known, for example.
In such a driving apparatus for a hybrid vehicle also, in some cases, the transmission apparatus carries out an upshift in a state where the accelerator pedal position is equal to or smaller than a prescribed value. In such a case also, the so-called clutch-to-clutch shifting is generally carried out and, accordingly, the release-side element is relatively swiftly released fully at an initial stage in the shifting operation, while the friction engagement element to be engaged is gradually engaged while slipping in the semi-engaged state. Here, the rotating electrical machine is structured to be capable of generating regenerative torque based on a deceleration request of the vehicle.
Meanwhile, as for a common vehicle having an engine as a sole driving force source, a hybrid vehicle in a situation where its rotating electrical machine does not produce regenerative torque, and the like, the negative torque affecting the input member is small in a situation where the accelerator pedal position is equal to or smaller than a prescribed value. Accordingly, in such cases, even when the general shifting control that involves the so-called clutch-to-clutch shifting is exerted, the rotation speed of the input member is only reduced by frictional forces attributed to the components of the engine and the like, and the variation in the rotational speed is moderate. Therefore, the occurrence of shift shock in engaging the to-be-engaged element poses little problem. However, in a situation where the transmission apparatus included in the driving apparatus for a hybrid vehicle of Japanese Patent Application Publication No. JP-A-2008-094332 upshifts while the accelerator pedal position is equal to or smaller than a prescribed value, the rotating electrical machine carries out regenerative braking in some cases if the brake is intentionally operated by the driver of the vehicle. In such a case, if the common clutch-to-clutch shifting is carried out, the relatively great negative torque (regenerative torque) output from the rotating electrical machine greatly reduces the rotation speed of the input member, i.e., invites a rapid variation, and thus the shift shock highly possibly occurs. Addressing this problem, the vehicular driving apparatus described in Japanese Patent Application Publication No. JP-A-2008-094332 is structured such that, when the rotating electrical machine regenerates, the magnitude of the negative torque output from the rotating electrical machine is limited to be equal to or smaller than a certain magnitude. This avoids a rapid reduction in the rotation speed of the input member drivably connected to the rotating electrical machine, thereby suppressing the occurrence of the shift shock in the vehicle.